The present invention relates to a sulfide polymer composition which can be used for molding a sliding member such as bearings, cams, toothed wheels, slide plates, guiding parts, etc., and to the sliding member molded by using the said composition.
For its excellent heat resistance, chemical resistance and moldability, a sulfide polymer (hereinafter referred to as PPS) has been increasing the utilization in recent years for the sliding member of OA machines, etc. However, a sliding member made of PPS shows unsatisfactory self-lubricating properties, low elongation and brittleness, so that in use of PPS for sliding member, it has been usually necessary to add a solid lubricant and reinforcements in order to enhance lubricating properties and strength of the sliding member.
Some of the sliding member composed of PPS, the solid lubricant and the reinforcements are disclosed in, for instance, Japanese Patent Application Laid-Open (Kokai) Nos. 50-119040 (1975) and 2-219849 (1990).
Japanese Kokai No. 50-119040 (1975) discloses a sliding member improved in strength and endowed with lubricating properties by blending uncalcined polytetrafluoroethylene having a molecular weight of not less than 3.times.10.sup.5 with PPS, and fibrillating and orienting the polytetrafluoroethylene in the molded product.
Japanese Kokai No. 2-219849 (1990) discloses a synthetic resin composition for a sliding member, comprising a homogeneous mixture of a synthetic resin with 5-60 wt % of polytetrafluoroethylene and 0.1-15 wt % of phosphate, and in Examples thereof, a sliding member obtained by injection molding a powdery mixture composed of polyphenylene sulfide with 30 wt % of polytetrafluoroethylene (Rublon L-5, produced by Daikin Industries, Ltd.) and phosphates (e.g., 5 wt % of magnesium phosphate, 5 wt % of barium phosphate, or 0.5 wt %, 5 wt %, 15 wt % or 20 wt % of lithium phosphate), is disclosed.
The sliding member disclosed in the prior art, particularly, the sliding member disclosed in Japanese Kokai No. 2-219849 (1990) are low in coefficient of friction at the time of restart of operation, stabilized in dynamic friction coefficient and excellent in wear resistance, but such sliding member is defective in tensile strength and elongation. There has, therefore, been strong request for offer of sliding members which are low in friction coefficient at the restart in interrupted operations, and also low and stable in dynamic friction coefficient, no increment in wear depth by rising a sliding speed, and high in tensile strength and elongation. Specifically, it has been desired to provide the sliding member which can satisfy all of the following requirements: a static friction coefficient of not more than 0.13, a dynamic friction coefficient of not more than 0.20, a maximum wear depth of not more than 15 .mu.m, a tensile strength of not less than 500 kg/cm.sup.2, and an elongation of not less than 1.3%.
As a result of the present inventor's earnest studies in order to obtain such sliding member, it has been found that by homogeneously mixing 3-40 wt % of polyethylene tetrafluoride (=polytetrafluoroethylene, hereinafter abbreviated as PTFE) having a forming-ability of a three-dimensional network structure, 5-40 wt % of granulated PTFE having a number average molecular weight of from not less than 2,000 to less than 300,000, 0.1-15 wt % of a phosphate(s) and the balance composed of PPS, and molding the resultant mixture, the obtained sliding member has a static friction coefficient of not more than 0.12, a dynamic friction coefficient of not more than 0.19, an wear depth of not more than 15 .mu.m, a tensile strength of not less than 500 kg/cm.sup.2 and an elongation of not less than 1.5%. The present invention has been attained on the basis of this finding.